The present invention relates to a fixing device, and more particularly relates to a fixing device of electromagnetic induction heating method.
The present invention also relates to an image forming apparatus having such a fixing device and to an image forming method for forming images by the image forming apparatus. The image forming apparatus includes, for example, electrophotographic copiers, printers, facsimiles and multi-function machines thereof.
As fixing devices of electromagnetic induction heating method, as shown in JP 2001-43965 A, JP 2001-60490 A and JP 2001-135470 A, there has conventionally been known a fixing device having a fixing roller and a pressure roller, which are in pressure contact with each other so as to form a nip section, and having an exciting coil placed along the fixing roller for heating a magnetic material layer (hereinbelow referred to as “heat generating layer”) of the fixing roller through electromagnetic induction by the exciting coil, transporting a sheet (recording paper) with a toner image attached thereto through the nip section, and melting and fixing the toner image on the sheet by heat generation in the fixing roller. In those documents, a degaussing coil is provided in regions corresponding to axial end sections of the fixing roller (which are herein referred to as “small size sheet non-passing regions”). When a maximum size sheet passes the regions, the degaussing coil is opened, whereas when a small size sheet passes the regions, the degaussing coil is closed so that changes of a magnetic flux by the exciting coil is cancelled in the regions (small size sheet non-passing regions) where the degaussing coil is placed, by which excessive temperature rise in the axial end sections of the fixing roller is prevented.